As a former motorkhana competitor through the RCCV: I would have been interested but apologies, I never noticed your posts.
Love the idea of an electric motorkhana special. That car must have scared a few/all of the fossil competitors!
Cheers
Bryce

Thanks. The torque is great for motorkhana as it is for other standing start forms of motor sport. I have struggled to strike a good suspension setup though. It is starting to come good.

My design is a bit of a compromise as I am not willing to give up hill climbs and khanacross in order to be outright competitive in motorkhana. So the resulting car is a bit big to be an outright contender for Motorkhana at a national level.

The main advantage with ICE motorkhana cars are packaging in the design. They can fit a proportionally big motor without needing a big fuel tank to feed it. In an electric motorkhana car you can certainly fit a big motor but then where do you mount the batteries to supply the required power. Of course you could scale it all down but it gets increasingly difficult to find enough space for the batteries. Because in a smaller vehicle the driver's weight becomes a bigger proportion of the total. Therefore you can't afford to reduce the motor and battery too much or you risk losing the torque advantage off the line. Mine is 450kg which makes it about 570kg with driver and 1000amps worth or torque. I do think it would be possible to build a motorkhana specific EV at around 350KG making the total 470kg with driver but I would need to reduce the power to around 600amps which roughly means a 40% reduction in acceleration off the line. For an outright motorkhana car ultra capacitors may be a good option as it would then be possible to achieve the same current and torque without the weight penalty.

Hi all, I will be competing at the Mt Cotton Hill climb tomorrow. It is an informal day but should still prove interesting with the torque of the Batt mobile. I haven't had much track time at Mt Cotton and it has been quite a few years. I will go on record as saying the following:
A sub 50 second run would be acceptable. A 46-49 second run would be good. A 43-45 second run would be excellent. Anything quicker that 43 seconds would be amazing.

I had a great day at the Mt Cotton hill climb. I only managed a 52 second lap which isn't too impressive but not too bad for a first attempt. I need to learn the track and get brave to achieve better times. But the main issue was brake bias. I need more brake power in the back. I had to brake way too early to make it through the tighter corners. This cost me plenty of time. I am investigating conversion options for the rear brakes.

Absolutely. It is a hoot. Even after shoving my nose in the nuts I cam away smiling. It might not have been the case if there was damage. Keeping the cost low and having fun are my main two objectives. Times and results are a secondary consideration. I would love to attend Mt Cotton more frequently but unfortunately they generally run on Saturdays which is a problem for me. The fact that I was able to maintain good corner speed was very satisfying. But the best outcome from the day was the identification of my key weakness which is insufficient rear brake power. It gives me confidence I can improve leading up to future events.

Thanks Bryce, Yes that is one of my goals, to make people realise the shift to EVs does not spell the end of grass roots motorsport.
Not much resistance. Some people just lack interest, and just walk past without more than a glance. Some are very interested. Some would even follow the same path but are often scared of the first steps or how to go about it.

From a competitor point of view there is not much to hate. All the fun is still there and without the fumes. But the real challenge for some motorsport is the lack of fire and brimstone for spectators. Many spectators are only there for the roar of the big ICE cars.

I am nervous about the governing body. So far they have nothing in their regulations about EVs. But I know there are discussions and I just hope they don't introduce some EV killer rule. I don't think they will do it specifically to kill EVs. But they may introduce a rule that is near impossible to satisfy or way too expensive for grass roots competitors like me. A couple I am specifically nervous about is the need for a lithium compatible extinguisher or a earth leakage system. The Earth Leakage devices I have seen that handle 172v and 1000amps would cost more than $5000 and would put at least a temporary halt to my progress. Please let me know if you know of an alternative.

Might be worth helping them along like we did with eFXC - the rules for that competition were still pretty open but we had basic safety considerations, including capacitor discharge at shut-down and the like.
I think most racers at the track were interested in the electric bikes too, but like most motorsport, there were no spectators, and the racers were all too busy with their own competition. It takes time, and lots of money...

Thanks, yes that is the system I have. As you say it does provide a warning and it would probably disconnect the contactor if a leak is detected but the precharge resistor would still complete the circuit. So it really depends how they write the rules. In other words if they stipulate something like "complete disconnection" I would have a challenge. Also if they were knowledgeable on EVs and stipulated some backup method to cover a sticking contactor that would also cause me a challenge.

I have offered input into their discussions but they have not been in touch.

Hi there Greg - these issues (and more) for custom built electric race cars are well addressed in the Formula SAE competition, which has had an e-car category for nearly 10 years now. (BTW: for those who have not heard of it - FSAE is an annual, international competition for university engineering students to design and build a race car to meet FSAE rules. The Australasian event will be held at Winton raceway in Victoria early Dec this year).

If the governing body for your event have any problems with working with formulating rules for electric specials - I'd suggest you refer them to the Society of Automotive Engineers re the FSAE event and rules for electric powered entries.

it does provide a warning and it would probably disconnect the contactor if a leak is detected but the precharge resistor would still complete the circuit. So it really depends how they write the rules.

It's generally good practice to have more than one contactor anyway, though not really a rule as such.

It's generally good practice to have more than one contactor anyway, though not really a rule as such.

Interesting. I assume the two would need to be in series? Otherwise a failure on one would not be compensated by the other.

Also would you be able to just have the Precharge resistor across one contactor and then have a circuit to ensure the contactor without the precharge resistor is always turned on before the other contactor?
Doing it that way would mean 0 voltage from one side of the contactors to the other. Then when the contactor without the precharge resistor is closed minimal current can flow. But the protection is still in place but I Can achieve full disconnection.

The risk would be if the contactor with the precharge resistor stuck and then closing the other contactor would potentially send a spike down the circuit.

Just coming back to this forum to see what was happening. Great to see you are getting some outings in the car! It seems a bit twitchy in some of the videos; maybe needs a slightly longer wheelbase? Also in one of the still photos, 169a, the rear RH spring looks to be just about "coil bound", so if that happens mid corner at any sort of speed the handling will go to crap real fast. Also camber gain on steering lock seems too great - there's just about nothing of the tyre left on the road in some shots, although it won't be carrying much load.

As far as the motorsport authorities go, I think CAMS would be stupid to not make allowances, and AASA seem to be more forgiving than CAMS. So you might not be eligible for trophies but as long as the basic safety is there you should get a run. After all, our petrol-based cars are hardly the epitome of safety.

Good work! I will follow your progress with interest. Please continue to share.

Just coming back to this forum to see what was happening. Great to see you are getting some outings in the car! It seems a bit twitchy in some of the videos; maybe needs a slightly longer wheelbase? Also in one of the still photos, 169a, the rear RH spring looks to be just about "coil bound", so if that happens mid corner at any sort of speed the handling will go to crap real fast. Also camber gain on steering lock seems too great - there's just about nothing of the tyre left on the road in some shots, although it won't be carrying much load.

As far as the motorsport authorities go, I think CAMS would be stupid to not make allowances, and AASA seem to be more forgiving than CAMS. So you might not be eligible for trophies but as long as the basic safety is there you should get a run. After all, our petrol-based cars are hardly the epitome of safety.

Good work! I will follow your progress with interest. Please continue to share.

Thanks Geoffozz. I am in between events for the moment. Next one is Aug 17. I will certainly post some updates then.
The car is twitchy when it is set to be twitchy. For motorkhanas that is exactly what is required. When I set it for other events it is quite manageable. It is mostly determined by rear tyre pressures and the height of the passive rear steering connector. The car is basically a motorkhana car, having a longer wheel base would be more stable for higher speed but it was always going to be a compromise for other events.

I get what you are saying about the spring short of having components custom made I am constrained by what is available. In the 18 month life of the car I have already been through 4 sets of rear springs. Some of which were harder and didn't bind but they were too hard. I haven't been able to find longer springs in a similar spring rate. I would certainly be keen to try something else if I can get them at a reasonable price. It really doesn't get close to binding in the higher speed events it is only in motorkhana where it doesn't matter much because there isn't any risk. At higher speed it doesn't lean anywhere close to the same.

Front geometry is an issue. I have gone through a multitude of combinations and the later setup is the closest but still far from perfect. The problem is geometry setting are not common knowledge. Sure you can find the odd bit of data individually about camber, caster, king pin inclination and weight distribution. But what I really need is a complete set of data from a singly well handling car with the same weight distribution as mine. One car might handle well with a certain caster and camber but another might be terrible because the weight distribution or king pin inclination are different. When you say "camber gain" it implies that caster is the problem. I kinda doubt the caster is too much. I am thinking that a bit more caster and a bit less static camber might be an improvement. It is extremely challenging as it is not something I can adjust at an event. Which means in the 18 month life of the car I have only had the opportunity for around 10 adjustments. The usual advice I receive is more camber and more caster to compensate for the lack of weight in the front. This kinda contradicts your comment. I'm not saying you're wrong as I am clearly not an expert. It is getting better but it is a drawn out process. I do think less starting/static camber and more caster might reduce the difference between the left and right contact patches. I am happy to hear any / all views.

I have made some adjustments to the front geometry. I lengthened the upper control arms by 10mm each side. This has reduced the static camber and also has the side effect of reducing the length difference between the upper and lower control arms which will decrease the camber gain mid corner. It will be a while before I can test it at speed but at low speed (on my driveway) it feels significantly heavier which I interpret as a good thing because it means there is more front grip. The effort required to turn the steering shouldn't be an issue when moving at a reasonable speed. I have also installed a roof and a bigger brake master cylinder in preparation for the rear brake upgrade. I'll provide another update once I have the rear brakes installed.